Through silicon via design for stacking integrated circuits

ABSTRACT

A three-dimensional (3D) integrated circuit (IC) and associated forming method are provided. In some embodiments, a second IC die is bonded to a first IC die through a second bonding structure and a first bonding structure at a bonding interface. The bonding encloses a seal-ring structure in a peripheral region of the 3D IC in the first and second IC dies. The seal-ring structure extends from the first semiconductor substrate to the second semiconductor substrate. The bonding forms a plurality of through silicon via (TSV) coupling structures at the peripheral region of the 3D IC along an inner perimeter of the seal-ring structure by electrically and correspondingly connects a first plurality of TSV wiring layers and inter-wire vias and a second plurality of TSV wiring layers and inter-wire vias.

REFERENCE TO RELATED APPLICATION

This Application is a Divisional of U.S. application Ser. No. 15/989,556, filed on May 25, 2018, the contents of which are hereby incorporated by reference in their entirety.

BACKGROUND

The semiconductor industry has continually improved the processing capabilities and power consumption of integrated circuits (ICs) by shrinking the minimum feature size. However, in recent years, process limitations have made it difficult to continue shrinking the minimum feature size. The stacking of two-dimensional (2D) ICs into three-dimensional (3D) ICs has emerged as a potential approach to continue improving processing capabilities and power consumption of ICs.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 illustrates a layout view of some embodiments of a three-dimensional (3D) integrated circuit (IC) with a plurality of through silicon via (TSV) coupling structures.

FIG. 2 illustrates a cross-sectional view of some embodiments of the 3D IC of FIG. 1.

FIG. 3 illustrates a cross-sectional view of some more detailed embodiments of the 3D IC of FIG. 1 in which a 3D IC is encompassed by the plurality of TSV coupling structures.

FIGS. 4-5 illustrate cross-sectional views of other embodiments of the 3D IC of FIG. 1 in which a plurality of pad structures is arranged in the plurality of TSV coupling structures.

FIGS. 6-16 illustrate a series of cross-sectional views of some embodiments of a method for manufacturing a 3D IC with a plurality of TSV coupling structures.

FIG. 17 illustrates a flowchart of some embodiments of the method of FIGS. 6-16.

DETAILED DESCRIPTION

The present disclosure provides many different embodiments, or examples, for implementing different features of this disclosure. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper”, and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device or apparatus in use or operation in addition to the orientation depicted in the figures. The device or apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly. Even more, the terms “first”, “second”, “third”, “fourth”, and the like are merely generic identifiers and, as such, may be interchanged in various embodiments. For example, while an element (e.g., a conductive wire) may be referred to as a “first” element in some embodiments, the element may be referred to as a “second” element in other embodiments.

One type of three-dimensional (3D) integrated circuit (IC) comprises a first IC die and a second IC die over the first IC die. The first and second IC dies are two-dimensional (2D) IC dies, and comprise respective semiconductor substrates, respective interconnect structures between the semiconductor substrates and respective bonding structures between the interconnect structures. The interconnect structures comprise alternating stacks of wiring layers (e.g., horizontal routing) and via layers (e.g., vertical routing). The bonding structures comprise respective bonding dielectric layers, respective redistribution layers, and respective bonding contacts. The bonding dielectric layers contact at a bonding interface between the first and second IC dies. The redistribution layers are sunken into the bonding dielectric layers and also contact at the bonding interface. The bonding contacts extend respectively from the redistribution layers to the interconnect structures.

The 3D IC further comprises a plurality of through silicon via (TSV) coupling structures comprising respective through silicon vias (TSVs) disposed through at least one substrate of the IC dies and a stack of TSV wiring layers and inter-wire vias electrically coupled to the respective TSVs. A passivation layer accommodates pad structures directly over the 3D IC to provide electrical coupling with the 3D IC respectively through the plurality of TSV coupling structures. However, the pad structures and/or the corresponding TSV coupling structures may be arranged all across a backside of the IC die according to metal wires' layout and connection needs. The TSV coupling structures cause a stress to transistor levels. Therefore, a “keep-out-zone” is established in the chip design indicating a minimum distance between the circuitry and the TSV coupling structures. A big amount of semiconductor substrate area is cleared as the “keep-out-zone” so as to accommodate a sufficient number of TSV coupling structures. This area consumption limits the chip shrinking ability and also contributes to the design and modeling complexity.

In view of the foregoing, various embodiments of the present application are directed towards a 3D IC in which a plurality of TSV coupling structures is arranged at a peripheral region of the 3D IC next to a seal-ring structure, and associated methods. For example, in some embodiments, a first IC die comprises a first semiconductor substrate, a first interconnect structure over the first semiconductor substrate, and a first bonding structure over the first interconnect structure. The first bonding structure comprises a redistribution layer and a bonding contact extending from the redistribution layer to the first interconnect structure. A second IC die is stacked and bonded to the first IC die. The second IC die comprises a second semiconductor substrate, a second bonding structure, and a second interconnect structure between the second semiconductor substrate and the second bonding structure. The second bonding structure contacts the first bonding structure at a bonding interface. A seal-ring structure is arranged in a peripheral region of the 3D IC in the first and second IC dies extending from the first semiconductor substrate to the second semiconductor substrate. A plurality of through silicon via (TSV) coupling structures is arranged in the peripheral region of the 3D IC along an inner perimeter of the seal-ring structure. The plurality of TSV coupling structures respectively comprises a through silicon via (TSV) disposed in the second semiconductor substrate and electrically coupling to the 3D IC through a stack of TSV wiring layers and inter-wire vias. Compared to a previous approach where the TSV coupling structure are disposed all across the backside of the 3D IC, by arranging the plurality of TSV coupling structure at the peripheral region of the 3D IC along an inner perimeter of the seal-ring structure, the “keep-out-zone” of the TSVs of the plurality of TSV coupling structures are reduced. Thus, the 3D IC can be further shrunk, and the design and modeling complexity can be reduced.

With reference to FIG. 1, a layout view 100 of a 3D IC 150 with a plurality of TSV coupling structures 152 is provided according to some embodiments. As illustrated, in a peripheral region 101 of the 3D IC 150, a seal-ring structure 102 laterally encloses the 3D IC 150 and extends laterally along the peripheral region 101 of the 3D IC 150. In some embodiments, the seal-ring structure 102 may comprise one or more conductive rings that receptively has a laterally continuous ring shape, for example, a first conductive ring 146 a and a second conductive ring 146 b separated from one another by a dielectric material.

A plurality of through silicon via (TSV) coupling structures 152 is arranged in the peripheral region 101 of the 3D IC along an inner perimeter of the seal-ring structure 102. The plurality of TSV coupling structures 152 are separated from the seal-ring structure 102 and separated from one another by the dielectric material, and respectively comprises a through silicon via (TSV) 126 electrically coupling to the 3D IC 150 through an interconnect structure 108.

In some embodiments, the first conductive ring 146 a may have a first lateral width w1 equal to a second lateral width w2 of the second conductive ring 146 b. The TSV coupling structure 152 may have a third lateral width w3 greater than the first lateral width w1 or the second lateral width w2. A first distance d1 between the first and second conductive rings 146 a, 146 b may be smaller than a second distance d2 between the second conductive ring 146 b and the TSV coupling structure 152.

With reference to FIG. 2, a cross-sectional view 200 of some embodiments of the peripheral region 101 of the 3D IC 150 of FIG. 1 is provided. As illustrated, a second IC die 104 b is disposed over a first IC die 104 a. The first and second IC dies 104 a, 104 b may comprise respective semiconductor substrates 106 a, 106 b. The semiconductor substrates 106 a, 106 b are spaced from one another, respectively under and over respective interconnect structures 108 a, 108 b. In some embodiments, the semiconductor substrates 106 a, 106 b are bulk substrates of monocrystalline silicon or some other semiconductor, some other type of semiconductor substrate, or a combination of the foregoing. Further, in some embodiments, the semiconductor substrates 106 a, 106 b have respective thicknesses that are different. For example, a first semiconductor substrate 106 a of the first IC die 104 a may have a first thickness T_(a) and a second semiconductor substrate 106 b of the second IC die 104 b may have a second thickness T_(b) smaller than the first thickness.

The respective interconnect structures 108 a, 108 b of the first and second IC dies 104 a, 104 b are between the semiconductor substrates 106 a, 106 b and are spaced from one another by bonding structures 132 a, 132 b (e.g. hybrid bonding layers). A first interconnect structure 108 a of the first IC die 104 a comprises a first interlayer dielectric (ILD) layer 110 a, first wiring layers 112 a, first inter-wire via layers 114 a, first TSV wiring layers 122 a, and first TSV inter-wire vias 124 a. Similarly, a second interconnect structure 108 b of the second IC die 104 b comprises a second ILD layer 110 b, second wiring layers 112 b, second inter-wire via layers 114 b, second TSV wiring layers 122 b, and second TSV inter-wire vias 124 b. The first and second ILD layers 110 a, 110 b may be, for example, silicon dioxide, a low κ dielectric, some other dielectric, or a combination of the foregoing. As used here, a low κ dielectric is a dielectric with a dielectric constant κ less than about 3.9. The first wiring layers 112 a are alternatingly stacked with the first inter-wire vias 114 a in the first ILD layer 110 a. The second wiring layers 112 b are alternatingly stacked with the second inter-wire vias 114 b in the second ILD layer 110 b.

The seal-ring structure 102 is arranged in the first and second IC dies 104 a, 104 b. The seal-ring structure 102 laterally encloses the 3D IC 150 (shown in FIG. 1) of the first and second IC dies 104 a, 104 b, and extends respectively from the first semiconductor substrate 106 a to the second semiconductor substrate 106 b, such that the seal-ring structure 102 defines a wall or barrier protecting the 3D IC 150. In various embodiments, the seal-ring structure 102 is made up of one or more conductive rings that are concentrically aligned. For example, the seal-ring structure 102 may comprise the first conductive ring 146 a and a second conductive ring 146 b. The seal-ring structure 102 may protect the 3D IC from a die saw singulating the first and second IC dies 104 a, 104 b and/or from gases diffusing into the first and second IC dies 104 a, 104 b from an ambient environment of the first and second IC dies 104 a, 104 b.

In some embodiments, the first conductive ring 146 a of the seal-ring structure 102 comprises a first stack of the wiring layers 112 a, 112 b and the inter-wire vias 114 a, 114 b disposed at an outmost region of the peripheral region 101 and connected by a first pair 142 of bonding structures. The first pair 142 of bonding structures may include components of the redistribution layers 118 a, 118 b and bonding contacts 120 a, 120 b. The first conductive ring 146 a may be electrically isolated from the semiconductor substrates 106 a, 106 b and spaced apart from the semiconductor substrates 106 a, 106 b by the first and second ILD layers 110 a, 110 b. The second conductive ring 146 b of the seal-ring structure 102 comprises a second stack of the wiring layers 112 a, 112 b and the inter-wire vias 114 a, 114 b, and connected to a first device contact 116 a that borders the first semiconductor substrate 106 a and a second device contact 116 b that borders the second semiconductor substrate 106 b. The second conductive ring 146 b may comprise a second pair 144 of bonding structures which may include components of the redistribution layers 118 a, 118 b, but omit bonding contacts. The second stack of the wiring layers 112 a and the inter-wire vias 114 a may be electrically isolated from the wiring layers 112 b and the inter-wire vias 114 b by the bonding dielectric layers 136 a, 136 b. Since at least one of the conductive rings 146 a, 146 b is defined with a pair of bonding structures 132 a, 132 b, the seal-ring structure 102 may define a continuous wall or barrier respectively from and to the semiconductor substrates 106 a, 106 b for robust reliability and performance.

The TSV coupling structure 152 is disposed at an inner side of the second conductive ring 146 b opposite to the first conductive ring 146 a. The TSV coupling structure 152 comprises a stack of TSV wiring layers 122 a, 122 b (e.g. horizontal routing) and TSV inter-wire vias 124 a, 124 b (e.g. vertical routing) connected by pairs of TSV redistribution layers 128 a, 128 b and TSV bonding contacts 130 a, 130 b. The TSV coupling structure 152 also comprises a TSV 126 touching a metal layer 122 t of the second interconnect structure 108 b and disposed through the second semiconductor substrate 106 b. The metal layer 122 t may be one of the horizontal metal lines of the interconnect structure 108 b that is closest to the second semiconductor substrate 106 b. The TSV 126 may be further connected to a pad structure 158 in a passivation layer 148 and a solder bump 140 (or other applicable structures) overlying the passivation layer 148 to provide electrical connections and bonding, contacting, or connecting structures. The pad structure 158 may facilitate electrical coupling between the 3D IC 150 and external devices or power source. The passivation layer 148 may be, for example, silicon dioxide, silicon nitride, silicon oxynitride, silicon carbide, some other dielectric, or a combination of the foregoing. Compared to a previous approach where the TSV coupling structure is arranged “randomly” all across the backside of the 3D IC according to interconnect structures' layout (e.g. according to the layout of the metal layer 122 t of the second interconnect structure 108 b), by re-routing and arranging some or all of the TSV coupling structures at the peripheral region of the 3D IC along an inner perimeter of the seal-ring structure, the “keep-out-zone” of the TSVs of the plurality of TSV coupling structures are reduced. Thus, the 3D IC can be further shrunk, and the design and modeling complexity can be reduced.

The first and second wiring layers 112 a, 112 b, the first and second inter-wire vias 114 a, 114 b, the first and second device contacts 116 a, 116 b, the TSV wiring layers 122 a, 122 b, the TSV inter-wire vias 124 a, 124 b, the TSV redistribution layers 128 a, 128 b, and TSV bonding contacts 130 a, 130 b are conductive and may be, for example, aluminum copper, copper, aluminum, tungsten, some other metal or conductive material, or a combination of the foregoing. In some embodiments, the first wiring layers 112 a are integrated respectively with, and/or the same materials respectively as, immediately underlying layers of the first inter-wire via and device contacts 114 a, 116 a. In other embodiments, the first wiring layers 112 a are distinct respectively from, and/or different materials respectively than, immediately underlying layers of the first inter-wire via and device contacts 114 a, 116 a. Similarly, in some embodiments, the second wiring layers 112 b are integrated respectively with, and/or the same materials respectively as, immediately overlying layers of the second inter-wire via and device contacts 114 b, 116 b. In other embodiments, the second wiring layers 112 b are respectively distinct from, and/or different materials respectively than, immediately overlying layers of the second inter-wire via and device contacts 114 b, 116 b.

The respective bonding structures 132 a, 132 b of the first and second IC dies 104 a, 104 b are between the interconnect structures 108 a, 108 b and contact at a bonding interface 134. The bonding structures 132 a, 132 b comprise respective bonding dielectric layer 136 a, 136 b, respective redistribution layers 118 a, 118 b, and respective bonding contacts 120 a, 120 b, TSV bonding contacts 130 a, 130 b. The bonding dielectric layers 136 a, 136 b contact at the bonding interface 134 to define a dielectric-to-dielectric interface. Further, the bonding dielectric layers 136 a, 136 b may be, for example, silicon dioxide, some other dielectric, or a combination of the foregoing.

The redistribution layers 118 a, 118 b and TSV redistribution layers 138 a, 138 b are recessed respectively into the bonding dielectric layers 136 a, 136 b, such that redistribution layers 118 a, 118 b and TSV redistribution layers 138 a, 138 b are respectively even with the bonding dielectric layers 136 at the bonding interface 134. Further, the redistribution layers 118 a, 118 b and TSV redistribution layers 138 a, 138 b contact at the bonding interface 134 to define a conductor-to-conductor interface, and are electrically coupled to the interconnect structures 108 a, 108 b, respectively, by the bonding contacts 120 a, 120 b and TSV bonding contacts 130 a, 130 b. The bonding contacts 120 a, 120 b and TSV bonding contacts 130 a, 130 b extend respectively from the redistribution layers 118 a, 118 b and TSV redistribution layers 138 a, 138 b respectively to the interconnect structures 108 a, 108 b. The redistribution layers 118 a, 118 b, TSV redistribution layers 138 a, 138 b, bonding contacts 120 a, 120 b and TSV bonding contacts 130 a, 130 b are conductive and may be, for example, aluminum copper, copper, aluminum, tungsten, some other conductive material, or a combination of the foregoing.

In some embodiments, a first redistribution layer 118 a of the first IC die 104 a is integrated with, and/or the same material as, a first bonding contact 120 a of the first IC die 104 a. In other embodiments, the first redistribution layer 118 a is distinct from, and/or a different material than, the first bonding contact 120 a. Similarly, in some embodiments, a second redistribution layer 118 b of the second IC die 104 b is integrated with, and/or the same material as, a second bonding contact 120 b of the second IC die 104 b. In other embodiments, the second redistribution layer 118 b is distinct from, and/or a different material than, the second bonding contact 120 b.

The seal-ring structure 102 is arranged in the first and second IC dies 104 a, 104 b. The seal-ring structure 102 laterally encloses the 3D IC 150 (shown in FIG. 1) of the first and second IC dies 104 a, 104 b, and extends respectively from the first semiconductor substrate 106 a to the second semiconductor substrate 106 b, such that the seal-ring structure 102 defines a wall or barrier protecting the 3D IC. For example, the seal-ring structure 102 may protect the 3D IC from a die saw singulating the first and second IC dies 104 a, 104 b and/or from gases diffusing into the first and second IC dies 104 a, 104 b from an ambient environment of the first and second IC dies 104 a, 104 b. Further, the seal-ring structure 102 is made up of one or more conductive rings that are concentrically aligned. For example, the seal-ring structure 102 may comprise the first conductive ring 146 a and a second conductive ring 146 b.

With reference to FIG. 3, a cross-sectional view 300 the 3D IC of FIG. 1 is provided in which the 3D IC 150 is shown encompassed by the plurality of TSV coupling structures 152 according to some embodiments. These embodiments may, for example, also be combined with the embodiments of FIGS. 1-2 and/or FIGS. 4-5 below, or a combination of the foregoing.

As illustrated, the first and second IC dies 104 a, 104 b are 2D IC dies and may comprise semiconductor device following different fabrication nodes and configured to operate at different voltage levels. For example, the first die 104 a may be a 28 nm die and operate at a relative low voltage level (e.g. 1V), while the second die 104 b may be a 55 nm die and operate at a relative high voltage level (greater than that of the first die 104 a, e.g. 1.1V, 6V, or 32V). the 3D IC 150 comprises one or more semiconductor devices 302 a, 302 b distributed between the semiconductor substrates 106 a, 106 b, and electrically coupled to one another with conductive paths defined by the interconnect structures 108 a, 108 b and the bonding structures 132 a, 132 b. The semiconductor devices 302 a, 302 b may be, for example, MOSFETs, IGFETS, MIM capacitors, flash memory cells, or the like. Further, in some embodiments, isolation regions 304 a, 304 b are arranged in the semiconductor substrates 106 a, 106 b to provide electrical isolation between the semiconductor devices 302 a, 302 b. The isolation regions 304 a, 304 b may be, for example, shallow trench isolation (STI) regions or deep trench isolation (DTI) regions.

With reference to FIG. 4, a cross-sectional view 400 of other embodiments of the peripheral region 101 of a 3D IC is provided, in which the TSVs 126 over the TSV coupling structure 152 have alternative shapes. These embodiments may, for example, also be combined with the embodiments of FIGS. 1-2 and/or the embodiments of FIG. 3.

As illustrated by the cross-sectional view 400 of FIG. 4, the passivation layer 148 comprises a first passivation sub-layer 148 a and a second passivation sub-layer 148 b overlying the first passivation sub-layer 148 a and further comprises a pad structure 158 in the first and second passivation sub-layers 148 a, 148 b. The first and second passivation sub-layers 148 a, 148 b are dielectric and may be, for example, silicon dioxide, silicon nitride, silicon oxynitride, silicon carbide, some other dielectric, or a combination of the foregoing. Further, the first and second passivation sub-layers 148 a, 148 b may be the same material or different materials.

The pad structure 158 is disposed directly overlying the TSV coupling structure 152. For example, the pad structure 158 may comprise a first pad structure 158 a as a via region and a second pad structure 158 b as a pad region directly on the first pad structure 158 a

The pad structure 158 a is conductive and may be, for example, copper, aluminum, aluminum copper, tungsten, some other conductor, or a combination of the foregoing. In some embodiments, the second pad structure 158 b is/are integrated with, and/or the same material as, the first pad structure 158 a. In other embodiments, the second pad structure 158 b is/are distinct from, and/or a different material than, the first pad structure 158 a. Further, in some embodiments, each of the second pad structure 158 b has a third width greater than that of each of the first pad structure 158 a.

Also illustrated by the cross-sectional view 400 of FIG. 4, a variant of FIG. 2 is provided in which the TSV 126 discretely tapers, such that sidewalls of the TSV 126 are discontinuous from the first pad structure 158 a to the metal layer 122 t. The TSV 126 comprises a backside substrate portion 126 b in the second semiconductor substrate 106 b and extending from a top surface of the second semiconductor substrate 106 b, through the second semiconductor substrate 106 b, to a bottom surface of the second semiconductor substrate 106 b. Further, the TSV 126 comprises a backside contact portion 126 a in the second ILD layer 110 b and extending from the bottom surface of the second semiconductor substrate 106 b to a TSV wiring layer 122 t nearest the second semiconductor substrate 106 b.

The TSV 126 is conductive and may be, for example, copper, aluminum, aluminum copper, tungsten, some other conductor, or a combination of the foregoing. In some embodiments, the backside substrate portion 126 b is integrated with, and/or the same material as, the backside contact portion 126 a. In other embodiments, the backside substrate portion 126 b is distinct from, and/or a different material than, the backside contact portion 126 a. Further, the backside substrate portion 126 b has a lateral width greater than that of the backside contact portion 126 a.

With reference to FIG. 5, a cross-sectional view 500 of other embodiments of the 3D IC is provided in which the coupling structures 152 may be disposed through the first semiconductor substrate 106 a, electrically connected to the first wiring layers 162 a of the first die, and electrically disconnected to the second wiring layers 162 b of the second die 104 b. These embodiments may, for example, also be combined with the embodiments of FIGS. 1-2 and/or the embodiments of FIG. 4. As illustrated by the cross-sectional view 500 of FIG. 5, as an example, one or multiple of the first TSV wiring layers 122 a may be electrically connected to corresponding first wiring layers 162 a. One or multiple of the second TSV wiring layers 122 b may be electrically isolated to the first TSV wiring layers 122 a and/or the second wiring layers 162 b. TSV bonding contacts may not present in the coupling structure 152.

With reference to FIGS. 6-16, a series of cross-sectional views 600-1600 illustrate some embodiments of a method for manufacturing a 3D IC with a seal-ring structure and a plurality of TSV coupling structures (see, e.g., FIG. 16). The 3D IC comprises a first IC die 104 a and a second ID die 104 b (see, e.g., FIG. 11) arranged over and hybrid bonded to the first IC die 104 a. Further, the seal-ring structure 102 is made up of a first seal-ring substructure 102 a (see e.g., FIG. 7) in the first IC die 104 a and a second seal-ring substructure 102 b (see, e.g., FIG. 11) in the second IC die 104 b. The plurality of TSV coupling structures 152 (see, e.g., FIG. 12) is respectively made up of a lower TSV coupling structures 152 a (see e.g., FIG. 7) in the first IC die 104 a and an upper TSV coupling structures 152 b (see, e.g., FIG. 11) in the second IC die 104 b.

As illustrated by the cross-sectional view 600 of FIG. 6, a pair of first ILD layers 110 a is formed over a first semiconductor substrate 106 a. For example, a lower layer of the first ILD layers 110 a is formed covering the first semiconductor substrate 106 a, and an upper layer of the first ILD layers 110 a is subsequently formed covering the lower layer. The first ILD layers 110 a are formed stacked and may, for example, be formed by vapor deposition (e.g., chemical or physical vapor deposition), atomic layer deposition, thermal oxidation, some other growth or deposition process, or a combination of the foregoing. Further, the first ILD layers 110 a may be formed of, for example, silicon dioxide, a low κ dielectric, some other dielectric, or the like.

In some embodiments, an etch stop layer (not shown) is formed between the lower and upper first ILD layers 110 a. The etch stop layer is a different material than the lower and upper first ILD layers 110 a and may be, for example, silicon nitride. Further, in some embodiments, the lower and upper first ILD layers 110 a are integrated together and/or are the same material. For example, the lower and upper first ILD layers 110 a may be different regions of the same deposition or growth.

As illustrated by the cross-sectional view 700 of FIG. 7, a first wiring layer 112 a and a first device contact 116 a are formed respectively in the first ILD layers 110 a. For example, the first wiring layer 112 a may be formed sunken into the upper layer of the first ILD layers 110 a, and the first device contact 116 a may be formed extending from the first wiring layer 112 a, through the lower layer of the first ILD layers 110 a, to the first semiconductor substrate 106 a. Further, the first wiring layer 112 a and the first device contact 116 a are formed with patterns of the first seal-ring substructure 102 a and the 4 lower TSV coupling structures 152 a.

In some embodiments, the process for forming the first wiring layer 112 a and the first device contact 116 a comprises performing a first selective etch into the upper layer of the first ILD layers 110 a to form first openings in the upper layer with a pattern of the first wiring layer 112 a. The first selective etch may stop, for example, on an etch stop layer between the first ILD layers 110 a. Thereafter, a second selective etch is performed into the lower layer of the first ILD layers 110 a to form second openings in the lower layer with a pattern of the first device contact 116 a. A conductive layer is formed filling the first and second openings, and a planarization is performed to coplanarize an upper or top surface of the conductive layer with an upper or top surface of the upper layer, whereby the first wiring layer 112 a and the first device contact 116 a are formed from the conductive layer. The first and second selective etches may be performed selectively by, for example, photolithography, and/or the planarization may be performed by, for example, chemical mechanical polish (CMP).

While the acts of FIGS. 6 and 7 illustrate and describe a dual-damascene-like process for forming the first wiring layer 112 a and the first device contact 116 a, a single-damascene-like process may alternatively be employed to form the first wiring layer 112 a and the first device contact 116 a in other embodiments. A dual-damascene-like process and a single-damascene-like process are respectively dual-damascene and single-damascene processes that are not restricted to copper.

As illustrated by the cross-sectional view 800 of FIG. 8, the acts of FIGS. 6 and 7 are repeated one or more times. As such, one or more additional first ILD layers 110 a are formed stacked over the first semiconductor substrate 106 a, each accommodating an additional first wiring layer 112 a and a first inter-wire via layer 114 a. Collectively, the first ILD layers 110 a, the first wiring layers 112 a, the first device contact 116 a, and the one or more first inter-wire via layers 114 a define a first interconnect structure 108 a.

As illustrated by the cross-sectional view 900 of FIG. 9, a pair of first bonding dielectric layers 136 a is formed over the first interconnect structure 108 a. For example, a lower layer of the first bonding dielectric layers 136 a is formed covering the first interconnect structure 108 a, and an upper layer of the first bonding dielectric layers 136 a is subsequently formed covering the lower layer. The first bonding dielectric layers 136 a may be formed, for example, in the same manner, or a similar manner as described for the first ILD layers 110 a in FIG. 6.

In some embodiments, an etch stop layer (not shown) is formed between the first bonding dielectric layers 136 a. The etch stop layer is a different material than the first bonding dielectric layers 136 a and may be, for example, silicon nitride. Further, in some embodiments, the first bonding dielectric layers 136 a are integrated together and/or are the same material. For example, the first bonding dielectric layers 136 a may be different regions of the same deposition or growth.

As illustrated by the cross-sectional view 1000 of FIG. 10, a first redistribution layer 118 a and first bonding contact 120 a, the first TSV bonding contact 130 a are formed in the first bonding dielectric layers 136 a respectively for the lower seal-ring structure 102 a and the lower TSV coupling structures 152 a. For example, the first redistribution layer 118 a may be formed sunken into an upper layer of the first bonding dielectric layers 136 a, and the first bonding contact 120 a may be formed extending from the first redistribution layer 118 a, through the lower layer of the first bonding dielectric layers 136 a, to the first interconnect structure 108 a. The first redistribution layer 118 a and the first bonding contact 120 a are formed with a pattern of the first seal-ring substructure 102 a. The first redistribution layer 118 a and the first bonding contacts 130 a are formed with a pattern of the lower TSV coupling structures 152 a. Collectively, the first bonding dielectric layers 136 a, the first redistribution layer 118 a, and the first bonding contact 120 a, the first TSV contact 130 a define a first bonding structure 132 a.

In some embodiments, the process for forming the first redistribution layer 118 a and the first bonding contacts 120 a and TSV bonding contacts 130 a is performed in the same manner or a similar manner as described for the first wiring layer 112 a and the first device contact 116 a in FIG. 7. Further, while the acts of FIGS. 9 and 10 illustrate and describe a dual-damascene-like process for forming the first redistribution layer 118 a and the first bonding contacts 120 a and TSV bonding contacts 130 a, a single-damascene-like process may alternatively be employed to form the first redistribution layer 118 a and the first bonding contacts 120 a and TSV bonding contacts 130 a in other embodiments.

As illustrated by the cross-sectional view 1100 of FIG. 11, the second IC die 104 b is formed with the second seal-ring substructure 102 b and the upper TSV coupling structures 152 b. The second IC die 104 b is formed in the same manner or a similar manner as described for the first IC die 104 a in FIGS. 6-10. As such, the second IC die 104 b comprises a second interconnect structure 108 b over a second semiconductor substrate 106 b, and further comprises a second bonding structure 132 b over the second interconnect structure 108 b. The second interconnect structure 108 b comprises a pair of second ILD layers 110 b, as well as a second wiring layer 112 b and a second device contact 116 b respectively in the second ILD layers 110 b. Further, the second interconnect structure 108 b comprises one or more additional pairs of second ILD layers 110 b stacked over the second semiconductor substrate 106 b, each accommodating additional second wiring layer 112 b and second inter-wire via layers 114 b. The second bonding structure 132 b comprises a pair of second bonding dielectric layers 136 b, as well as a second redistribution layer 118 b and a second bonding contact 120 b respectively in the second bonding dielectric layers 136 b.

As illustrated by the cross-sectional view 1200 of FIG. 12, the second IC die 104 b is flipped and bonded to the first IC die 104 a, such that the first and second bonding structures 132 a, 132 b interface to define a hybrid bond (HB). The HB comprises a dielectric-to-dielectric bond between the first and second bonding dielectric layers 136 a, 136 b. Further, the HB comprises a conductor-to-conductor bond between the first and second redistribution layers 118 a, 118 b. Collectively, the first and second seal-ring substructures 102 a, 102 b define the seal-ring structure 102. Collectively, the first and second TSV coupling structures 152 a, 152 b define the TSV coupling structures 152. The process of bonding the second IC die 104 b to the first IC die 104 a may comprise, for example, fusion bonding processes and/or metallic bonding processes.

As illustrated by the cross-sectional view 1300 of FIG. 13, a planarization is performed on the second semiconductor substrate 106 b to thin the second semiconductor substrate 106 b to a thickness T_(b). The planarization may be performed by, for example, a CMP and/or an etch back.

As illustrated by the cross-sectional view 1400 of FIG. 14, a series of selective etches is performed into the second semiconductor substrate 106 b to form a backside semiconductor opening 1402 and a backside contact opening 1404 directly over the TSV coupling structures 152. The backside semiconductor opening 1402 and the backside contact opening 1404 are formed extending to a metal layer 122 t of the second wiring layer 112 b nearest the second semiconductor substrate 106 b, thereby exposing the second wiring layer 112 b. The backside contact opening 1404 has a width that is less than that of the backside semiconductor opening 1402. The selective etch may be performed selectively by, for example, photolithography. Then, a TSV 126 is formed filling the TSV opening 1302. The TSV 126 is conductive and may be formed of, for example, aluminum, copper, aluminum copper, some other conductive material, a combination of the foregoing, or the like. In some embodiments, the process for forming the TSV 126 comprises forming a conductive layer filling the TSV opening 1302 and covering the second semiconductor substrate 106 b. The conductive layer may, for example, be formed by vapor deposition, atomic layer deposition, electrochemical planting, some other growth or deposition process, or a combination of the foregoing. Thereafter, a planarization is performed into the conductive layer to coplanarize an upper or top surface of the conductive layer with an upper or top surface of the second semiconductor substrate 106 b, thereby forming the TSV 126. The planarization may be performed by, for example, CMP.

As illustrated by the cross-sectional view 1500 of FIG. 15, a passivation layer 148 is formed covering the second semiconductor substrate 106 b and the TSV 126, and a pad structure 158 is formed through the passivation layer 148 reaching the TSV 126. The passivation layer 148 may, for example, be formed by vapor deposition (e.g., chemical or physical vapor deposition), atomic layer deposition, thermal oxidation, some other growth or deposition process, or a combination of the foregoing. Further, the passivation layer 148 may be formed of, for example, silicon dioxide, silicon nitride, some other dielectric, a combination of the foregoing, or the like. The passivation layer 148 may comprise a first passivation sub-layer 148 a and a second passivation sub-layer 148 b over the first passivation sub-layer 148 a. The pad structure 158 is formed through the first and second passivation sub-layers 148 a, 148 b. The pad structure 158 comprises a first pad structure 158 a extending through the first passivation sub-layer 148 a to the TSV 126 and a second pad structure 158 b extending through the second passivation sub-layer 148 b to the first pad structure 158 a. A planarization (e.g., a CMP) may be performed into the pad structure 158 to coplanarize an upper or top surface of the pad structure 158 with an upper or top surface of the second passivation sub-layer 148 b.

As illustrated by the cross-sectional view 1600 of FIG. 16, a polymer layer 156 is formed covering the passivation layer 148 and the pad structure 158. A solder bump 140 is formed overlying the polymer layer 156 to provide electrical connections. The solder bump 140 may be made of metal material such as gold.

With reference to FIG. 17, a flowchart 1700 of some embodiments of the method of FIGS. 6-16 is provided.

At 1702, a first IC die with a lower seal-ring structure and a plurality of lower TSV coupling structures is formed. The lower seal-ring structure has a ring-shape and is arranged in a peripheral region of the first IC die. The plurality of lower TSV coupling structures is arranged in the peripheral region of the first IC die along an inner perimeter of the lower seal-ring structure. See, for example, FIGS. 6-10.

At 1704, a second IC die with an upper seal-ring structure and a plurality of upper TSV coupling structures are formed. The upper seal-ring structure has a ring-shape and is arranged in a peripheral region of the second IC die. The plurality of upper TSV coupling structures is arranged in the peripheral region of the second IC die along an inner perimeter of the upper seal-ring structure. The positions of the upper seal-ring structure and the plurality of upper TSV coupling structures correspond to positions of the lower seal-ring structure and the plurality of lower TSV coupling structures. See, for example, FIG. 11.

At 1706, the second IC die is flipped and bonded to the first IC die, such that the upper seal-ring structure and the plurality of upper TSV coupling structures are directly over and contacts the lower seal-ring structure and the plurality of lower TSV coupling structures at a bonding interface between the first and second bonding structures. See, for example, FIG. 12.

At 1708, a plurality of through substrate vias (TSVs) is formed in the second semiconductor substrate directly over the corresponding plurality of TSV coupling structures. See, for example, FIG. 14. In some embodiments, forming the TSVs is preceded by thinning the second semiconductor substrate. The thinning may be performed by, for example, a planarization, such as CMP. See, for example, FIG. 13.

At 1710, a pad structure and a solder bump are formed directly over the plurality of TSV. See, for example, FIGS. 15-16.

While the flowchart 1700 of FIG. 17 is illustrated and described herein as a series of acts or events, it will be appreciated that the illustrated ordering of such acts or events are not to be interpreted in a limiting sense. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein. Further, not all illustrated acts may be required to implement one or more aspects or embodiments of the description herein, and one or more of the acts depicted herein may be carried out in one or more separate acts and/or phases.

In view of the foregoing, some embodiments of the present application provide a method of forming a 3D IC. A first IC die is provided with a first semiconductor substrate, a first interconnect structure over the first semiconductor substrate, a first bonding structure over the first interconnect structure, and a first plurality of TSV wiring layers and inter-wire vias. A second IC die is provided with a second semiconductor substrate, a second bonding structure, a second interconnect structure between the second semiconductor substrate and the second bonding structure, and a second plurality of TSV wiring layers and inter-wire vias. The second IC die is bonded to the first IC die through a second bonding structure and a first bonding structure at a bonding interface. The bonding encloses a seal-ring structure in a peripheral region of the 3D IC in the first and second IC dies. The seal-ring structure extends from the first semiconductor substrate to the second semiconductor substrate. The bonding forms a plurality of through silicon via (TSV) coupling structures at the peripheral region of the 3D IC along an inner perimeter of the seal-ring structure by electrically and correspondingly connects a first plurality of TSV wiring layers and inter-wire vias and a second plurality of TSV wiring layers and inter-wire vias.

Further, other embodiments of the present application provide a method for manufacturing a 3D IC. A first IC die is formed with a lower seal-ring structure and a plurality of lower TSV coupling structures arranged in a peripheral region of the first IC die. Forming the first IC die comprises forming a first interconnect structure over a first semiconductor substrate, a first bonding contact and a first TSV bonding contact over the first interconnect structure, and a first redistribution layer over the first bonding contact and a first TSV redistribution layer over the first TSV bonding contact. The first interconnect structure, the first bonding contact, and the first redistribution layer are formed defining the lower seal-ring structure, and the first interconnect structure, the first TSV bonding contact, and the first TSV redistribution layer are formed defining the lower TSV coupling structure. A second IC die is formed with an upper seal-ring structure and a plurality of upper TSV coupling structures corresponding to the lower seal-ring structure and the plurality of lower TSV coupling structures. Forming the second IC die comprises forming a second interconnect structure over a second semiconductor substrate, a second bonding contact over the second interconnect structure and a second redistribution layer over the second bonding contact. The second interconnect structure, the second bonding contact, and the second redistribution layer are formed defining the upper seal-ring structure, and wherein the second interconnect structure, the second TSV bonding contact, and the second TSV redistribution layer are formed defining the upper TSV coupling structure. The second IC die is flipped and bonded to the first IC die, such that the upper seal-ring structure contacts the lower seal-ring structure at a bonding interface between the first and second redistribution layers to form a seal-ring structure, and the plurality of upper TSV coupling structures contacts the plurality of lower TSV coupling structures at the bonding interface to form a plurality of TSV coupling structure.

Further yet, other embodiments of the present application provide a method for manufacturing a 3D IC. A first IC die and a second IC die are prepared separately. The first and second IC dies are formed with respective semiconductor substrates, respective interconnect structures between the semiconductor substrates, and respective bonding structures between the interconnect structures. The interconnect structures comprise alternating stacks of wiring layers and via layers; wherein the bonding structures comprise respective bonding dielectric layers, respective redistribution layers, and respective bonding contacts; wherein the bonding dielectric layers contact at a bonding interface between the first and second IC dies, wherein the redistribution layers are in the bonding dielectric layers and contact at the bonding interface, and wherein the bonding contacts extend respectively from the redistribution layers respectively to the interconnect structures. The first IC die and the second IC die are bonded face to face, enclosing a seal-ring structure at a peripheral region of the first and second IC dies, wherein the seal-ring structure extends respectively from and to the semiconductor substrates to define a barrier around an interior of the first and second IC dies. The bonding also encloses a plurality of through silicon via (TSV) coupling structures along an inner perimeter of the seal-ring structure, wherein the plurality of TSV coupling structures respectively includes a plurality of through silicon via (TSV) in the semiconductor substrate of the second IC die and a plurality of stacks of TSV wiring layers and inter-wire vias. The seal-ring structure is formed with a first conductive ring and a second conductive ring that are concentric to one another, wherein a bonding contact and a redistribution layer are present at the first conductive ring and are absent from the second conductive rings.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A method for manufacturing a three-dimensional (3D) integrated circuit (IC), comprising: providing a first IC die comprising a first semiconductor substrate, a first interconnect structure over the first semiconductor substrate, a first bonding structure over the first interconnect structure, and a first plurality of TSV wiring layers and inter-wire vias; providing a second IC die comprising a second semiconductor substrate, a second bonding structure, a second interconnect structure between the second semiconductor substrate and the second bonding structure, and a second plurality of TSV wiring layers and inter-wire vias; bonding the second IC die to the first IC die through the second bonding structure and the first bonding structure at a bonding interface, the bonding enclosing a seal-ring structure in a peripheral region of the 3D IC in the first and second IC dies, wherein the seal-ring structure extends from the first semiconductor substrate to the second semiconductor substrate; and wherein the bonding forms a plurality of through silicon via (TSV) coupling structures at the peripheral region of the 3D IC along an inner perimeter of the seal-ring structure by electrically connecting the first plurality of TSV wiring layers and inter-wire vias and the second plurality of TSV wiring layers and inter-wire vias; wherein the plurality of TSV coupling structures are each discretely arranged along the inner perimeter of the seal-ring structure.
 2. The method according to claim 1, further comprising forming a through silicon via (TSV) in the second semiconductor substrate, wherein the TSV is electrically coupled to one of the plurality of TSV coupling structures.
 3. The method according to claim 1, wherein the plurality of TSV coupling structures are formed to respectively define a conductive path through a pair of bonding contacts, respectively from the first interconnect structure to the second interconnect structure.
 4. The method according to claim 1, wherein the first interconnect structure is formed by forming a first interlayer dielectric (ILD) layer, first wiring layers, and first via layers, wherein the first wiring layers and the first via layers are alternatingly stacked in the first ILD layer; and wherein the second interconnect structure is formed by forming a second ILD layer, second wiring layers, and second via layers, wherein the second wiring layers and the second via layers are alternatingly stacked in the second ILD layer.
 5. The method according to claim 4, wherein the first bonding structure is formed by forming a first bonding dielectric layer, a first redistribution layer and a first bonding contact extending from the first redistribution layer to the first interconnect structure; wherein the second bonding structure is formed by forming a second bonding dielectric layer, a second redistribution layer and a second bonding contact extending from the second redistribution layer to the second interconnect structure; and wherein the first bonding dielectric layer contacts the second bonding dielectric layer at the bonding interface to define a dielectric-to-dielectric interface, wherein the first redistribution layer contacts the second redistribution layer at the bonding interface to define a conductor-to-conductor interface.
 6. The method according to claim 5, wherein the seal-ring structure is formed by forming a first conductive ring and a second conductive ring along an inner perimeter of the first conductive ring and spaced apart from the first conductive ring by the first and second ILD layers and first and second bonding dielectric layers.
 7. The method according to claim 6, wherein the first conductive ring is formed by forming a first stack of the first interconnect structure and the second interconnect structure connected by the first and second redistribution layers and bonding contacts, wherein the first conductive ring is electrically isolated from the first and second semiconductor substrates; and wherein the second conductive ring is formed by forming a second stack of the first interconnect structure and the second interconnect structure connected respectively to first and second device contacts, wherein the first interconnect structure and the second interconnect structure of the second stack is electrically isolated from one another by the bonding dielectric layers.
 8. The method according to claim 7, wherein the plurality of TSV coupling structures is formed by forming multiple stacks of the first interconnect structure and the second interconnect structure connected by discrete portions of a TSV redistribution layer and discrete portions of a TSV bonding contact, wherein the plurality of TSV coupling structures is electrically coupled to devices of the 3D IC.
 9. The method according to claim 1, further comprising: forming a passivation layer covering the first and second IC dies; and forming a plurality of pad structures directly over the plurality of TSV coupling structures, wherein the plurality of pad structures extends through the passivation layer to the second semiconductor substrate.
 10. The method according to claim 9, further comprising: forming a through substrate via (TSV) extending through the second semiconductor substrate contacting with the pad structure and the second interconnect structure, wherein sidewalls of the TSV are continuous from the pad structure to the second interconnect structure.
 11. The method according to claim 9, further comprising: forming a through substrate via (TSV) extending through the second semiconductor substrate, wherein sidewalls of the TSV are discontinuous from the pad structure to the second interconnect structure.
 12. The method according to claim 1, further comprising: forming a three-dimensional (3D) IC circuitry arranged in the first and second IC dies, wherein the seal-ring structure encloses the 3D IC circuitry so as to protect the 3D IC circuitry, and the plurality of TSV coupling structures laterally encompass the 3D IC circuitry and electrically coupled to the 3D IC circuitry.
 13. A method for manufacturing a three-dimensional (3D) integrated circuit (IC), the method comprising: forming a first IC die with a lower seal-ring structure and a plurality of lower TSV coupling structures arranged in a peripheral region of the first IC die, wherein forming the first IC die comprises forming a first interconnect structure over a first semiconductor substrate, a first bonding contact and a first TSV bonding contact over the first interconnect structure, and a first redistribution layer over the first bonding contact and a first TSV redistribution layer over the first TSV bonding contact, and wherein the first interconnect structure, the first bonding contact, and the first redistribution layer are formed defining the lower seal-ring structure, and wherein the first interconnect structure, the first TSV bonding contact, and the first TSV redistribution layer are formed defining the lower TSV coupling structure; forming a second IC die with a upper seal-ring structure and a plurality of upper TSV coupling structures corresponding to the lower seal-ring structure and the plurality of lower TSV coupling structures, wherein forming the second IC die comprises forming a second interconnect structure over a second semiconductor substrate, a second bonding contact and a second TSV bonding contact over the second interconnect structure, and a second redistribution layer and a second TSV redistribution layer over the second bonding contact, and wherein the second interconnect structure, the second bonding contact, and the second redistribution layer are formed defining the upper seal-ring structure, and wherein the second interconnect structure, the second TSV bonding contact, and the second TSV redistribution layer are formed defining the upper TSV coupling structure; and flipping and bonding the second IC die to the first IC die, such that the upper seal-ring structure contacts the lower seal-ring structure at a bonding interface between the first and second redistribution layers to form a seal-ring structure, and the plurality of upper TSV coupling structures contacts the plurality of lower TSV coupling structures at the bonding interface to form a plurality of TSV coupling structures; wherein the plurality of lower TSV coupling structures are each discretely arranged along an inner perimeter of the lower seal-ring structure.
 14. The method according to claim 13, wherein forming the first interconnect structure comprises forming an alternating stack of via layers and wiring layers over the first semiconductor substrate, wherein the first bonding contact is formed over and contacting a top one of the wiring layers, and wherein the first redistribution layer is formed over and contacting the first bonding contact.
 15. The method according to claim 13, wherein the first IC die is formed such that the plurality of TSV coupling structures respectively defines a conductive path from the first semiconductor substrate to the second semiconductor substrate.
 16. The method according to claim 13, further comprising: forming a passivation layer covering the first and second IC dies; performing a first etch into the passivation layer to form a plurality of pad openings directly over the plurality of TSV coupling structures, wherein the pad openings expose the second semiconductor substrate; and forming and patterning a plurality of pad structures filling the pad openings.
 17. The method according to claim 13, further comprising: performing an etch into the second semiconductor substrate and the second interconnect structure to form a plurality of via openings, wherein the plurality of via openings exposes wiring layers in the second interconnect structure and is directly over the plurality of TSV coupling structures; forming a plurality of through substrate vias (TSVs) filling the via openings with an upper surface that is even with an upper surface of the second semiconductor substrate; forming a passivation layer over the second semiconductor substrate and the TSVs; and forming and patterning a plurality of pad structures directly over the TSVs, wherein the plurality of pad structures overhangs the passivation layer and extends through the passivation layer to the TSVs.
 18. The method according to claim 13, further comprising: performing a first etch into the second semiconductor substrate to form a plurality of semiconductor openings, wherein the plurality of semiconductor openings is directly over the plurality of TSV coupling structures; performing a second etch into the second interconnect structure, through the plurality of semiconductor opening, to form a plurality of contact openings, wherein the plurality of contact openings exposes wiring layers in the second interconnect structure and has a smaller width than the plurality of semiconductor openings; and forming a plurality of through substrate vias (TSVs) filling the semiconductor and pad openings with an upper surface that is even with an upper surface of the second semiconductor substrate.
 19. The method according to claim 18, further comprising: forming a passivation layer over the second semiconductor substrate and the TSVs; and forming a plurality of pad structures directly over the plurality of TSVs, wherein the plurality of pad structures overhangs the passivation layer and extends through the passivation layer to the TSVs.
 20. A method for manufacturing a three-dimensional (3D) integrated circuit (IC), comprising: prepare a first IC die and a second IC die separately, wherein the first and second IC dies are formed with respective semiconductor substrates, respective interconnect structures between the semiconductor substrates, and respective bonding structures between the interconnect structures; wherein the interconnect structures comprise alternating stacks of wiring layers and via layers; wherein the bonding structures comprise respective bonding dielectric layers, respective redistribution layers, and respective bonding contacts; wherein the bonding dielectric layers contact one another at a bonding interface between the first and second IC dies, wherein the redistribution layers are in the bonding dielectric layers and contact at the bonding interface, and wherein the bonding contacts extend respectively from the redistribution layers respectively to the interconnect structures; bonding the first IC die and the second IC die face to face, enclosing a seal-ring structure at a peripheral region of the first and second IC dies, wherein the seal-ring structure extends respectively from and to the semiconductor substrates to define a barrier around an interior of the first and second IC dies; and wherein the bonding also encloses a plurality of through silicon via (TSV) coupling structures along an inner perimeter of the seal-ring structure, wherein the plurality of TSV coupling structures respectively includes a plurality of through silicon via (TSV) in the semiconductor substrate of the second IC die and a plurality of stacks of TSV wiring layers and inter-wire vias; wherein the seal-ring structure is formed with a first conductive ring and a second conductive ring that are concentric to one another, wherein a bonding contact and a redistribution layer are present at the first conductive ring and are absent from the second conductive ring. 